The direct current (D.C.) motor is often called upon to do the really tough industrial jobs because of its flexibility and because it is easy to control. It can also provide its full rated output torque at start up, i.e., zero RPM, using no more than its rated current. In certain applications, however, its high starting torque can be problematic, such as when a D.C. motor is used to drive mechanical devices that do not stand up well to high starting torque. Precise speed control can also be difficult to achieve as the load on a D.C. motor changes.
U.S. Pat. No. 6,144,179 to Kessler et al. entitled “Method for Establishing the Rotational Speed of Mechanically Commutated D.C. Motors” discloses a method and apparatus for providing precise speed control using commutation ripple. For various reasons, however, the commutation ripple of some D.C. motors is not detectable, rendering the method and apparatus disclosed in the patent unhelpful. A method and apparatus for providing precise control of a D.C. motor rotation speed when commutation ripple is too weak or undetectable would be an improvement over the prior art.